1. Field of the Invention
This invention pertains to a control system for an automatic transmission, and more particularly relates to such a system for controlling the operation of clutches and gear shift actuators.
2. Description of the Prior Art
Preselective transmissions eliminate the need for hand shifting of sliding gear transmissions by permitting the vehicle operator to select for subsequent operation any of the gear ratios of the transmission and later to set the transmission for operation in that selected gear ratio. Shifting of the gears is accomplished either mechanically through a linkage connecting the clutch pedal to the shift lever of the transmission or by means of a solenoid or vacuum power unit that employs inlet manifold vacuum and a small lever, usually mounted on the steering post. The operator can select any gear other than the one in current use and then by momentarily depressing a clutch pedal, the change to the selected gear occurs spontaneously as the pedal is released.
A transmission that operated on this general principle produced the low forward speed from a simple planetary gearset, and the second and third forward speeds by compounding the various gear trains. For the fourth speed, or direct drive, a cone clutch was adapted to engage the brake drum of the third speed, whereby the entire gear assembly was locked together and rotated as a unit with the driving and driven shafts.
In this transmission, the brake for a selected gear was contracted on the drum by a spring force transmitted through the brake band and through a toggle mechanism. This mechanism included a lever bar or bus bar mounted on knife edges, to which an angular motion was imparted by the spring and which was connected to the gear pedal by a linkage. Gear change was made by depressing the pedal, which compressed the spring and released the band on the drum of the gear that has been in use. When the bus bar moved to the release position, the operating strut of the gear, which had been preselected, moved into engagement with the bus bar. When the vehicle operator then released the pedal and the brake contracted on the drum by the spring, the preselected gear ratio was made.